Higher unbranched primary alcohols, i.e. those containing 6 to 20 carbon atoms, are extensively used as intermediates in the chemical industry. For instance, C.sub.8 - to C.sub.12 -alcohols are esterified with phthalic acid to produce plasticizers distinguished by good low-temperature flexibility. Sodium salts of n-alkyl sulfates, which are obtained by esterification of concentrated sulfuric acid with unbranched fatty alcohols, are biologically degradable and consequently have acquired great importance as environmentally compatible synthetic detergents. Esters based on straight-chain primary alcohols and branched dicarboxylic acids are valuable lubricants which are used, in particular, in aircraft engines.
The examples of uses for straight-chain primary alcohols given above explain the great interest in processes for their preparation which start from inexpensive raw materials and which can be carried out with great technical simplicity. A further requirement is that the straight-chain feedstocks not isomerize in the course of preparation and that, where it is possible for secondary and/or tertiary alcohols to form along with the desired primary alcohols, clear preference is given to the latter.
In accordance with DE-C-2 855 421, C.sub.9 -alcohols are prepared by dimerization of butenes in the presence of organoaluminum compounds as catalysts to give an octene mixture; thereafter, the mixture is hydroformylated. The resultant C.sub.9 -alcohols are reacted with phthalic acid to form dinonylphthalate plasticizers.
By hydroformylation of a butene fraction, aldol condensation of the resulting aldehyde mixture, and subsequent hydrogenation, C.sub.10 -alcohols are obtained which are processed further by the process described in EP-A 366 089 to give esters of phthalic acid.
Another route to obtain didecyl phthalate mixtures is described in EP-A-424 767. The esters are prepared in a multistage process by dimerization of butene mixtures, hydroformylation and hydrogenation of the resulting octene mixture to give a nonanol mixture, and dehydration of the nonanol mixture to form a mixture of nonenes. This mixture is hydroformylated and hydrogenated to form a decanol mixture, which is then esterified to produce the desired product.
The known methods still fail to meet all of the economic and technical demands made on a process carried out on the industrial scale. For instance, the starting materials are not always available in sufficient quantity or at favorable cost, or their conversion to the desired straight-chain alcohols requires complex processes.